Change all --insensitive flags to --ignore-case (#7198)

# Description

Support for this breaking change was raised in #7191. This affects
`sort`, `sort-by`, `str contains` and `find`. `--ignore-case` is used by
a few POSIX programs such as `less` and `grep`, as well as a few other
popular utils like `tree` and `wget`. Since long names aren't especially
popular (existing primarily for self-documentation purposes), I consider
this on the shallow end of the compat-break scale.

Note that the `-i` short flag is not affected.
 
# User-Facing Changes

See above.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace --features=extra -- -D warnings -D
clippy::unwrap_used -A clippy::needless_collect` to check that you're
using the standard code style
- `cargo test --workspace --features=extra` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/strings/str_/contains.rs

@@ -37,7 +37,7 @@ impl Command for SubCommand {
                 SyntaxShape::CellPath,
                 "For a data structure input, check strings at the given cell paths, and replace with result",
             )
-            .switch("insensitive", "search is case insensitive", Some('i'))
+            .switch("ignore-case", "search is case insensitive", Some('i'))
             .switch("not", "does not contain", Some('n'))
             .category(Category::Strings)
     }
@@ -62,7 +62,7 @@ impl Command for SubCommand {
         let args = Arguments {
             substring: call.req::<String>(engine_state, stack, 0)?,
             cell_paths,
-            case_insensitive: call.has_flag("insensitive"),
+            case_insensitive: call.has_flag("ignore-case"),
             not_contain: call.has_flag("not"),
         };
         operate(action, args, input, call.head, engine_state.ctrlc.clone())